This invention relates to a process for improving the thermal stability of copper base alloys having a low stacking fault energy. This thermal stability is evident in an improvement in both the creep resistance and the stress relaxation resistance of the alloys. It is a desirable objective to be able to process copper base alloys in such a manner so as to provide suitable spring properties for use in electrical connectors and like components. The properties of the materials which are required for obtaining suitable performance in electrical contactors or connectors are diverse. Aside from stress corrosion and electrical conductivity requirements specifically applicable to most parts of this type, they also require that either good contact be maintained during service or that a given stress produce a given deflection. In most of these parts the load is cycled and, as a consequence on reloading, the previously mentioned requirements must still be met.
It is known that materials can exhibit a time dependent strain under a stress that is below the yield strength as determined by engineering methods or as restrained may undergo a reduction stress. The former characteristic is called creep and the latter characteristic is referred to as stress relaxation. In spring loaded parts, it is therefore a desirable feature of an alloy system that it exhibit high creep resistance and high stress relaxation resistance under the highest desirable loads possible.
U.S. Pat. No. 3,841,921 teaches that stress relaxation resistance and creep resistance of low stacking fault energy copper base alloys can be improved by a low temperature thermal treatment. Such a treatment provides an improvement in the stiffness characteristics of the low stacking fault energy alloys.